- A new endpoint `/v1/agent/service/:service_id` which is a generic way to look up the service for a single instance. The primary value here is that it:
- **supports hash-based blocking** and so;
- **replaces `/agent/connect/proxy/:proxy_id`** as the mechanism the built-in proxy uses to read its config.
- It's not proxy specific and so works for any service.
- It has a temporary shim to call through to the existing endpoint to preserve current managed proxy config defaulting behaviour until that is removed entirely (tested).
- The built-in proxy now uses the new endpoint exclusively for it's config
- The built-in proxy now has a `-sidecar-for` flag that allows the service ID of the _target_ service to be specified, on the condition that there is exactly one "sidecar" proxy (that is one that has `Proxy.DestinationServiceID` set) for the service registered.
- Several fixes for edge cases for SidecarService
- A fix for `Alias` checks - when running locally they didn't update their state until some external thing updated the target. If the target service has no checks registered as below, then the alias never made it past critical.
* Rename agent/proxy package to reflect that it is limited to managed proxy processes
Rationale: we have several other components of the agent that relate to Connect proxies for example the ProxyConfigManager component needed for Envoy work. Those things are pretty separate from the focus of this package so far which is only concerned with managing external proxy processes so it's nota good fit to put code for that in here, yet there is a naming clash if we have other packages related to proxy functionality that are not in the `agent/proxy` package.
Happy to bikeshed the name. I started by calling it `managedproxy` but `managedproxy.Manager` is especially unpleasant. `proxyprocess` seems good in that it's more specific about purpose but less clearly connected with the concept of "managed proxies". The names in use are cleaner though e.g. `proxyprocess.Manager`.
This rename was completed automatically using golang.org/x/tools/cmd/gomvpkg.
Depends on #4541
* Fix missed windows tagged files
